My electrochemistry is rusty (heh…a joke). If I apply a DC voltage to two stainless steel electrodes in regular hard water, what will happen at the electrodes? I know water will be split into hydrogen and oxygen gas, but I suspect the electrodes will also be chewed up…maybe one of them even releasing chromium.
Can you also clarify/define for me the cathode and the anode? I think for an electrolytic cell where voltage is applied, the cathode is negative…Is that right?
Depends on the applied voltage, temperature, the size / area of the electrodes , hard water type, etc. etc.
In general, The anode will have a reducing environment and the cathode an oxidizing environment. So - rust will form on cathode and rust will turn back to iron on anode (in general).
Yes Chromium will be oxidized on cathode (the electrode connection to the negative of the battery)
Yes.
This appears to disagree with you about the cathode oxidizing the electrode material
Is it wrong, or am I just terribly confused.
Oh…just so I’m sure. The cathode (negative terminal) is where Hydrogen gas will be formed in addition to the OH- ion.
You are right, i confused it. The mnemonic is Red Cat an Ox. Reduction at Cathode and Oxidation at Anode. Sorry.
Further question than. If OH- is formed at the cathode during electrolysis of water…where does the counter ion come from? One certainly couldn’t take a sample at the cathode and collect an unbalanced amount of hydroxyl ions without a counter positive ion in the mix.
I know it takes a bit of time for the positive ions formed at the anode to travel through the water to balance the charge of the hydroxyl ion; but I’m not really accepting that someone could legitimately collect a surplus of hydroxyl ions at the cathode as they are being produced resulting in an overall negatively charged sample of water.
Where does the counter ion come from so my beaker of hydroxyl ions doesn’t scoot across the table and crash into my beaker of positive ions?
What counterion? The ions not being neutrally balanced is the whole point.
The negative charge is taken up by the cathode. There are no surplus hydroxyls. The hydroxyls combine with themselves, and the excess electrons go up the wire. If they couldn’t go up the wire, you wouldn’t have a circuit in the first place.
Ions aren’t magnets.
OP may benefit from this diagram:
https://www.nature.com/articles/s41598-020-80683-6/figures/1
Note that’s with a polymer electrolyte, but you’d mentioned hydroxyls, so this forces them to be the charge carrier. And for whatever reason it’s not showing water at the cathode, which this one (right side) does:
https://chemistry-europe.onlinelibrary.wiley.com/cms/asset/df92d95e-a7ce-4f34-bcf2-d3a35c008a0c/celc202001329-toc-0001-m.jpg
If we’re balancing with base, hydroxyl is produced by the reduction of water at the cathode, with concomitant oxidation of hydroxyl at the anode.